Compression molding and injection molding are common techniques for molding solid fiber reinforced plastic products. Such products typically have 5 to 50 percent by weight fibrous material, with the remainder being a plastic resin material, and these products usually have a density greater than about 5 pounds per cubic foot (pcf). Compression molding is also used to form molded fibrous insulation products, which typically have a density less than about 5 pcf. Such molded fibrous insulation products include thermal insulation for mechanical applications, such as pipe insulation and duct insulation, as well as acoustical and thermal insulation products for such applications as appliances and automobiles. The fibers for these fibrous insulation products include mineral fibers, such as glass fibers, as well as polymer fibers, such as polyethylene terephthalate (pet) or polypropylene (pp) fibers. The fibrous insulation products made with mineral fibers typically include a heat settable binder material in an amount within the range of from about 5 percent to about 20 percent by weight. The fibrous insulation products made with polymer fibers often do not include binder material, relying on fiber-to-fiber bonding for the structural integrity of the product.
The molded fibrous insulation products are formed by placing a fibrous molding media into a mold having heated upper and lower mold bodies, and closing the mold. The heat from the mold bodies sets or cures the binder, where a binder is present, thereby forming the fibrous insulation product with the desired shape, density and stiffness for the intended product application. Where a binder is not present, as with a polymer fiber insulation product, the heat from the mold bodies bonds the polymer fibers together where they intersect with each other, thereby forming the fibrous insulation product with the desired shape, density and stiffness for the intended product application. The heat transfer process from the mold body surface to the fibrous molding media is primarily by conduction and radiation. This heat transfer into and through the fibrous molding media during the molding process cannot be controlled easily.
During the molding of the fibrous insulation product the surface of the fibrous molding media assumes the shape of the surface of the upper and lower mold bodies. It can be appreciated that the surface or contour of the upper and lower mold bodies must be changed when it is desired to mold a fibrous insulation product of different shapes. This requires changing the mold bodies for each different desired insulation product. Typically it takes a considerable amount of time and money to make new molds with the desired contours. The changing of mold surfaces can be simplified by using changeable or replaceable mold inserts within the upper and lower mold bodies. However, it would be advantageous if the process and apparatus for molding fibrous insulation products could be further improved.